Method of producing thin enameled dials.



\ niniirn saarras rarer EDGAR L; HULL, OF W'ALTHAM, MASSACHUSETTS, ASSIGNOB T0 WALTHAW WATCH COMPANY, OF WALTHAM, MASSACHUSETTS, A CORPORATION OF MASSACHUfiETTS.

No Drawing.

Specificationofletters Patent.

Patented June 6, 1911..

Application filed. November 8, 1910. Serial No. 591357.

which the following is a specification.

The present invention relates to theart of watch-making and consists in a step by which a thinner-watch may be produced.

Dcvelopn'ients in the watch-making art have tended, 111 one direction, toward the production of watches of decreasing, thickness with substantially the same diameter,

the object. being to produce a watch which will be large enough to be accurate as a time keeper and to be easily read, without taking much room in the wearers pocket. One

step in this direction has been to make the dial of metal and secure it flat against, the top plate of the watch movement. thereby at one stroke materially diminishing the thickness of the entire watch. There are many respects, however, in which an enameled dial is more desirable than a plain metal dial, but up to the present time it. has not been possible to produce a-' thin enameled dial'or to mountsuch a dial very close to the frame plate of the watch movement.

The purpose of my invention is to provide a watch dial which is enameled on its face and at the same time is approximately as thin as a metal dial and may be secured to the watch movement plate as closely as a metal dial.

The reason for the impossibility which has hitherto existed ofjsccuring enameled dials closely to the watch plates is that the enamel with which the back of the plate has been coated is uneven, presenting" lumps where an excess of the enamel in its fluid form has gathered, and forming fillets by capillary action around the bases of the pins by which such dials are secured to the movemcnts.

My invention resides in a method of makthe dials flat on their back faces and freefrom such lumps and fillets.

In order to understand my invention it should be known in the first place that enameled dials are made in the first place from thin metal carrying a coating of enamel which is applied-in the usual mannor in a finely divi ed condition mixed with a fluid binder or vehicle and afterward fused by the action of heat. The dials must be enameled on both sides prior to firing, because if coated on onl one side, they warp and the enamel is liable to crackin cooling, owing to the unequal coefficient of expansion of the metal and enamel. Hence, before being fired, the forms the foundation enameled on its under side or back with a layer of the enamel and then on its face with another layer. The back of the dial plate is first coated and the plate is then held horizontal while the face coating is applied. The dial is also held in this position while being fired in order that the face coating may be of even thickness and have a smooth surface. The same positio'n of the dialwhich insures the even thickness of the face coating, however, causes the coating on the back to be uneven because,- owing to its fluid condition, any excess is liable to gather in incipient drops. Also capillary actioncauses the fluid enamel.to use around the pins by which the dial is attachedto the movement plate and to prevent entrance of such pins sutliciently far into the holes made for their reception in the movement'plate.

Attempts have been made prior to my invention to produce thin watch dials enameled on their faces, and at the same time capable of being placed closely against the watch plates by applying the enamel in the first instance only to their faces. Such attempts have always been unsuccessful for the reasons heretofore noted, that the dials are liable to warp and the enamel to crack. According to my invention I secure the results so long sought by first coating the dials with enamel in the usual manner on both faces and then after the same has been fused by firing, removing the coat of enamel from the back, leaving the face intact- The removal of the rear coating is effected by dipping the dial into hydrofluoric acid and keeping it immersed therein long enough metal plate, which of the dial, is-first to effect the desired purpose, the enamel coating. of the face being preserved by a covering of wax. or other material having equivalent properties as to resisting the action of the. acid. War. is named in this connection as being the material preferably employed, because of the ease-with which it may be applied and removed. It isto be understood that in this term I include all substances of a waxy or greasy nature, but I wish it to be also understood that I do not limit myself to such substances. Neither do I limit my inventien to the acid treatment for removing the coating of enamel from the back, since other modes of removing this coating may be employed, within the spirit of the invention.

After treatment as heinbeiore described, the dial has the even smooth face coating of enamel and a metal backing from which the attaching pins project free from the obstructing enamel. The dial is perfectly fiat, having been preserved in this condition by the back coating while being fired, and in the subsequent cooling, and the face coating is free from cracks. The back of the metal plate is also smooth and the angles between the same and the pins are sharp and free of enamel obstructions, so that the dial may rest flat against the watch plate when the pins are in the sockets.

I claim,

1. The method of producing thin enameled watch dials which consists in provid ing' both surfaces of a metal plate with coatings of enamel, fusing or firing, the coated plate and removing the coating on the back of the plate.

2. The method of producing thin fiat watch dials enameled on one side only, Which consists in applyin a coat of enamel of uniform thickness to t e face of a metal plate which forms the body of the dial, preserving the plate and enamel coating in a flat condition and free from cracks during the steps of firing and cooling, by the application of a coating of enamel to the back of plying a. protecting enamel coat to the back of a metal dial plate, upon the face of which a dial coating has been applied, to protect the plate from warping and cracking the face when being fired and cooled, covering the face of the dial with a substance unaffected by hydrofluoric acid, leaving the back unprotected, and immersing the dial in hydrofluoric acid whereby the coating on i the back is removed.

In testimony whereof I haXe affixed my signature, in presence of two Witnesses.

EDGAR L. HULL. Witnesess:

OLoF OI-ILSON, OsoAn H. BUTLER.

the plate and removing the enamel from the 

